This application is hereby cross referenced to related applications, Ser. No. 283,470. filed July 15, 1981, Ser. No. 299,325, filed Sept. 4, 1981 and Ser. No. 493,289, filed Aug. 10, 1983, all assigned to the same assignee.
In my prior copending application Ser. No. 147,602, filed May 7, 1980, now U.S. Pat. No. 4,373,598 owned by the same assignee, there is disclosed a piston which returns rotary valve members to a neutral position under operating pressure. Thus, such a neutral return position is subjected during steering to the operating pressure in the pressure chamber to a servomotor adjacent to an end of the piston and which pressure acts on one face of the piston. In addition, a centering spring is utilized adding to the piston return force. These forces act through a cam device whereby rotating of a steering wheel by a vehicle operator is resisted by the pressure on the neutral return piston and the spring force, through the cam device to effect a simulated steering resistance of the vehicle wheels which are then being hydraulically powered.
Hydraulic boost is effected in the usual way by relative rotation between a rotary valve plug and the valve sleeve effected by the above-mentioned cam device. The relative rotation brings into action coacting grooves of the valve members for flow control of pressure and exhaust to the pressure chambers of a servomotor having a piston coupled by mechanical steering mechanism to vehicle wheels.
In such arrangements, the vehicle operator must exert a force to be stored in axle geometry; the additional force added in the course or steering brings the vehicle wheels back to straight ahead position. Accordingly, such systems require larger initial steering forces. The restoring forces for the vehicle wheels to straight ahead position is generally brought about by such axle geometry as, kingpin inclination.
Since in the steering operation a force over and above the necessary steering force must be added to store a return force in the axle geometry, initially larger steering forces have heretofore been required.